Steel bar stock and method for making same

ABSTRACT

A high strength fine grain killed steel consisting essentially of, by weight percent:   AND PROCESSED INTO BAR STOCK BY THE STEPS WHICH INCLUDE, HOT REDUCING TO SUBSTANTIALLY FINAL GAUGE, RAPIDLY COOLING THE HOT REDUCED STOCK, COLD FINISHING UP TO ABOUT 15%, AND STRESS RELIEVING BETWEEN ABOUT 500* AND 850* F. Said steel has particular utility for threaded bolts, such as &#39;&#39;&#39;&#39;U&#39;&#39;&#39;&#39; bolts, as the ductility is relatively high, permitting thread rolling and forming without additional heat treatment and cleaning.

[ 1 Sept. 9, 1975 STEEL BAR STOCK AND NIETHOD FOR MAKING SAME [76]Inventor: Hugh M. Gallagher, Jr., 7262 State Rd., Cincinnati, Ohio 45230[22] Filed: Dec. 29, 1972 [21] Appl. No.2 319,499

[52] US. Cl 148/12 B; 148/12 B [51] Int. Cl C2ld 7/02 [58] Field ofSearch 148/12 B, 36; 75/123 N, 75/123 J [56] References Cited UNITEDSTATES PATENTS 2,933,424 4/1960 Canney et a1. 148/12 B 3,230,118 l/l966Tufts 3,668,020 6/1972 Lucht 148/12 B Primary ExaminerW. StallardAttorney, Agent, or FirmMelville, Strasser, Foster & Hoffman [5 7]ABSTRACT A high strength fine grain killed steel consisting essentiallyof, by weight percent:

carbon 0.50 0.55% manganese 1.20 1.65% phosphorus 0.040% max. sulfur0.050% max. silicon 0.30% max. vanadium 0.03 0.05% iron Balance,

and processed into bar stock by the steps which include, hot reducing tosubstantially final gauge, rapidly cooling the hot reduced stock, coldfinishing up to about 15%, and stress relieving between about 500 and850 F. Said steel has particular utility for threaded bolts, 'such as Ubolts, as the ductility is relatively high, permitting thread rollingand forming without additional heat treatment and cleaning.

, -6'Claims, No Drawings STEEL BAR STOCK AND METHOD FOR MAKING SAMEBACKGROUND OF THE INVENTION The present invention relates to a highstrength steel in bar stock form, and more particularly to the use ofsaid steel in threaded fasteners, such as U bolts.

This development arose from a need in the automotive industry for arelatively low cost, high strength steel having a sufficiently highductility to permit thread rolling and forming into a U shape. Suchmembers, in nominal sizes ranging from A to 1 /2 inches, are used infasteningthe springs to the axles of trucks and automobiles. Since highstrength and good fatigue properties are obvious prerequisites for suchthreaded fasteners, it was necessary for the automotive industry to turnto the alloy steels such as AISI Type 4140. However, the material andprocessing costs for said steels are quite high, particularly whencompared with such costs for the steels of this invention.

In any case, the minimum mechanical and quality requirements forexternally threaded fasteners under SAE .l429d, for Grade 8 screws andstuds in sizes between A; and 1 /2 inches, are as follows:

Tensile Strength (psi) 150,000 Yield Strength (psi) 130,000 Elongationin 2" (7U 12 Reduction in Area 7!) 35 Hardness (Re) 32 38.

As noted above, it was necessary to use alloy steels, such as AISI Type4140 (Quenched and Tempered) to achieve these minimum requirements. Theuse of this material meant following a processing sequence not suitedfor developing maximum economy. For example, due to the undesirabilityof cut threads, which practice can materially affect the fatigueproperties of the bar stock, a roll threading step had to be followed.As a consequence, said operation had to be conducted prior to the quenchand temper, which necessitated a cleaning and often straightening beforeuse could be made of the bolt.

The present invention avoids these inherent problems by a combination ofchemistryand processing controls.

SUMMARY OF THE INVENTION The present invention contemplates a simplifiedpro.-

cessing sequence to produce a high strength, fine grained, killed steelbar stock, more particularly bar stock for use as threaded fasteners.

The steel of this invention is basically a medium high carbon steel, andconsists essentially of about, by weight percent, the following:

carbon 0.50 0.5591 manganese 1.20 401.65% phosphorus 0.040% max. sulfur0.050'71 max. silicon 0.3071 max. vanadium 0.03 0.05% iron Balance.

However, chemistry alone is not the answer, as a controlled processingsequence must be followed.

Briefly, in the practice of this invention, a steel having the foregoingchemistry is subjected to various metallurgical operations whichinclude. hot rolling the steel DETAILED DESCRIPTION OF THE PREFERREDEMBODIMENT This invention relates to a killed steel consistingessentially of, by weight percent:

carbon 0.50 0,55%

manganese l .20 l .657: phosphorus 0.0407 max. sulfur 0.050% max.silicon 0.15 0.30% vanadium 0.03 l 0.05% iron Balance.

which when processed into bar stock in the manner to be describedhereinafter, will have a fine grained structure between about A.S.T.M.No. 5-8, and meet the following minimum properties:

Tensile Strength (psi) 150,000 Yield Strength (psi) 130,000 Elongationin 2" ('7!) 12 Reduction in area (7U 35 Hardness (Rc) 32 38.

Before discussing the processing sequence in detail, it should be notedthat the preceding minimum properties are those required for Grade 8material under SAE Standard J429d. This SAE Standard covers themechanical and quality requirements for steel bolts, screws, studs, andsems used in automotive and related industries in sizes to 1 /2 inches,inclusive.

In todays age, where high speed personal transporta tion is quitecommon, one clear and essentialiequiIement is that the transportationmeans, such as truck, automobile, bus, etc., be as safe as practicalconsiderations will allow. But alongwith this, such means must beeconomical, or the vehicle would remain nothing more than a drawingboard concept. The present invention recognizes this, for it relates toa cost cutting material suitable for use in assembling the vehicles,without jeopardizing the safe performance thereof. v I

Turning now to the processing sequence, in the prac tice of thisinventionQa steel, preferably having a chem istry falling within theranges above, and preferably one having a minimum of 1.50% by weight Mn,is subjected to a standard hot reducing operation to within 10% to 15%of final gauge. However. instead of coiling the hot reduced bar stock,following s'aid hot reduction, the stock is cut or severed intoindividual lengths for rapid air cooling. This is in contrast to theslow cooling of a wound coil of hot steel. It was discovered with saidhigh carbon steels, that with rapid cooling, the formation of pearlitecould be avoided. However, as cooling rates decreased, the tendency forpearlite formation increased.

The individual lengths of hot reduced bar stock are then subjected to acold finishing to final gauge.

[t was then discovered that contrary to what would be pected, asignificant increase in, properties could be alized .with a controlledstress relieving step. Specifilly, it was found that the yield strengthcould be in- :ased by as mueh as 20,000 psi with a stress relief be- 5een about, 500 F. and about 850 F... for about 1 'ur. This may bedemonstrated by the comparison iich follows. v i 9 EXAMPLES I m A heatof steel, whose chemistry is as follows, by

right percent: 1

carbon 7 0.51%

manganese l 57% phosphorus 0.013% .l 5

sulfur 0.033%

silicon 0.30 71 vanadium 0.043%

iron Balance.

is processed in the preferred manner above into .680 20 :h rounds, andsubsequently stress relieved over a nge of temperatures. The results, asexpressed in meanical properties, are listed below:

'4 hot r' e'du'cing to within' 10% to of finaLgauge in straight lengths,a killed ferrous alloy consisting essentially of carbon between about0.50 0.55% by weight, manganese between about 1.20 1.65% by weight,vanadium between abo ut.0.03 0.05% by weight, with the balancesubstantially all iron, cold finishing said hot reduced stock to. finalgauge, and stress relieving said stock at a temperature between about500 F. 850 F.

2. The method according to claim 1 including the step of roll threadingthe stress relieved bar stock to form threaded fasteners. I Y I 3. Themethod according to claim I wherein said hot reduced bar stock israpidly cooled to avoid any substantial formation of pearlite.

4. The method according to claim 3 wherein said hot reduction isconducted as a continuous step, whereas the cold finishing is conductedon cut lengths of said hot reduced bar stock. 1

5. The method of making an automotive U-bolt in sizes up to about 1 /2inches diameter, comprising the steps of hot reducing to within 10% to15% of final gauge. in straight lengths, a medium high carbon steel,

The preceding data clearly shows the significance of e critica l stressrelief given the steels of this invenin'. However,it should beemphasized that said results e due in part to the chemistry of thesteel. For exame, several companion heats, having no vanadium andinta'inirig lesser amounts of manganese, were treated o n g with thelast samples above, and found to be relalely low in mechanicalproperties. Specifically, the tter could not meet the SAE standard notedabove. Since modifications may be made in the'processing "the steels ofthis invention, particularly by the skilled orker after readingthe'se'specifications, no limitation intended to be imposed hereinexcept as set forth in e appended claims. i i The embodiments'of theinvention in which an exclu- /e property or privilege is claimed aredefined as folws: I l l. A method of making ferrous bar stock in sizesup about 1%: inches diameter, comprising the steps of s are averagesfrom up to four samples grain sizes between about A.S.'I'.M. No. 5

cold finishingsaid hot reducedstock to final gauge, stress relievingsaid stock at a temperature between about 500 F, and 850 F., cuttingsaid stock to length.

thread rolling, and then cold forming said cut and threaded lengths intoUshape.

26. The method of making an automotive U-bolt in sizes up to about 1 /2inches diameter, comprising the steps of hot reducing to within 10% to15% of final gauge. in straight lengths, a killed ferrous alloyconsisting essentially of carbon between about 0.50% and 0.5 5% byweight, manganese between about 1.20% and 1.65% by weight, vanadiumbetween about 0.03% and 0.05% by weight, with the balance substantiallyall iron, cold finishing said hot reduced stock to final gauge,stressrelie'ving said stock at a temperature between about 500 F. and850 E., cutting said stock to length, thread rolling, and then coldforming said cut and threaded lengths into U-shape.

1. A METHOD OF MAKING FERROUS BAR STOCK IN SIZES UP TO ABOUT 11/2 INCHESDIAMETER, COMPRISING THE STEPS OF HOT REDUCING TO WITHIN 10% OF 15% OFFINAL GUAGE IN STRAIGHT LENGTHS, A KILLED FERROUS ALLOY CONSISTINGESSENTIALLY OF CARBON BETWEEN ABOUT 0.50 - 0.55% BY WEIGHT, MANGANESEBETWEEN ABOUT 1.20 1.65% BY WEIGHT, VANADIUM BETWEEN ABOUT 0.03 - 0.05%BY WEIGHT, WITH THE BALANCE SUBSTANTIALLY ALL IRON, COLD FINISHING SAIDHOT REDUCED STOCK TO FINAL GUAGE, AND STRESS RELIEVING SAID STOCK AT ATEMPERATURE BETWEEN ABOUT 500*F - 850*F.
 2. The method according toclaim 1 including the step of roll threading the stress relieved barstock to form threaded fasteners.
 3. The method according to claim 1wherein said hot reduced bar stock is rapidly cooled to avoid anysubstantial formation of pearlite.
 4. The method according to claim 3wherein said hot reduction is conducted as a continuous step, whereasthe cold finishing is conducted on cut lengths of said hot reduced barstock.
 5. The method of making an automotive U-bolt in sizes up to about1 1/2 inches diameter, comprising the steps of hot reducing to within10% to 15% of final gauge, in straight lengths, a medium high carbonsteel, cold finishing said hot reduced stock to final gauge, stressrelieving said stock at a temperature between about 500* F. and 850* F.,cutting said stock to length, thread rolling, and then cold forming saidcut and threaded lengths into U-shape.
 6. The method of making anautomotive U-bolt in sizes up to about 1 1/2 inches diameter, comprisingthe steps of hot reducing to within 10% to 15% of final gauge, instraight lengths, a killed ferrous alloy consisting essentially ofcarbon between about 0.50% and 0.55% by weight, manganese between about1.20% and 1.65% by weight, vanadium between about 0.03% and 0.05% byweight, with the balance substantially all iron, cold finishing said hotreduced stock to final gauge, stress relieving said stock at atemperature between about 500* F. and 850* E., cutting said stock tolength, thread rolling, and then cold forming said cut and threadedlengths into U-shape.